A bandgap voltage circuit is a temperature independent voltage reference circuit widely used in integrated circuits. For example, an analog-to-digital converter (ADC) may have at least two inputs, namely a voltage to be measured and a reference voltage. A bandgap voltage generated by the bandgap voltage circuit may be provided to the ADC as the reference voltage for a full scale comparison for the voltage to be measured.
Generally, in the bandgap voltage circuit, two bipolar junction transistors (BJTs) may operate at different current densities and generate different base-emitter junction voltages. Difference between these different base-emitter junction voltages may have a proportional to absolute temperature (PTAT) dependency. By using these base-emitter junction voltages generated by different BJTs, a first order temperature independent voltage may be generated. However, such bandgap voltage circuit requires a high supply voltage (e.g., of about 1.5 Volts or higher), uses a large area (e.g., because of the associated BJT matching requirement), and may have inaccuracies caused by various associated circuits. Accordingly, it would be desirable and useful to provide an improved way of providing a reference voltage.